Three-dimensional monopole - a new ion trap mass analyser with one-dimensional ion sorting

This article describes an axially symmetric ion trap with one‐dimensional ion sorting (‘three‐dimensional (3D) monopole’). The mass spectrometer can be created by substituting one hyperboloid endcap electrode with a cone‐shaped electrode, the vertex of the cone coincides with the cross‐over point of the asymptotes of the ion trap electrodes. The potential applied to this cone‐shaped electrode is equal to the potential at the centre of the electrode system. The stability zone of the 3D monopole has a shape of a narrow band extending along the z boundary; the mass resolution and the quality factor (the product of resolution and sensitivity) are constant within this stability band which also lowers the requirements for the driving voltage stability. The mass resolution obtained 1s 100 measured at 50% peak height and the relative sensitivity is 3 × 10−5. Copyright © 2000 John Wiley & Sons, Ltd.